The loss of ozone over the Arctic varies widely from year to year, US scientists say.

The Arctic ozone loss during the nineties wasn't linked to chlorine - it's been driven by the meteorology

Dr Neil Harris, Eorcu

Using data collected by the US space agency (Nasa), they say the amount, timing and pattern of ozone loss all fluctuate.

They say their findings will help to show the effectiveness of agreements on limiting ozone depletion.

And they should also give scientists a better understanding of what is happening in the Arctic.

The research team, which analysed data from the Microwave Limb Sounder (MLS) on Nasa's Upper Atmosphere Research Satellite (UARS), report their findings in the Journal of Geophysical Research, published by the American Geophysical Union.

Ozone, a form of oxygen, protects all life on Earth against harmful ultraviolet radiation. Close to the poles it is thinning, largely because of reactions with chlorofluorocarbons (CFCs) and other industrial gases.

The ozone "hole" - more accurately a thinning - is worse over the Antarctic, where colder conditions mean the loss is more pronounced than in the Arctic.

Scientists believe the international agreement on ozone protection, the Montreal Protocol, should see it restored by about the middle of the century.